This invention relates to valve stems for medicinal aerosol products and the manufacture of such devices.
Pressurized metered dose aerosol delivery devices, such as metered dose inhalers (MDIs), allow a patient to self-administer individual metered doses of aerosolized medicine. A typical metered dose aerosol valve includes a metering chamber and a valve stem that slides through a diaphragm, also known as an outer stem gasket or seal, into the metering chamber. When not in use, the diaphragm maintains a closed seal around the valve stem. The valve stem includes a side hole in communication with a passageway inside the valve stem. When actuated, the side hole slides past the diaphragm and into the metering chamber. The side hole and passageway thus provide an outlet through which the metered dose of aerosol escapes the metering chamber. In the case of an MDI, the aerosolized medicine escapes the metering chamber and becomes accessible for oral or nasal inhalation by the patient.
The seal formed between the valve stem and the diaphragm gasket is critical. The diaphragm, typically made from an elastomeric material, must a) maintain the seal with the valve stem in order to prevent leakage of the aerosol formulation, and b) permit smooth, reliable valve operation. Leakage alters the relative concentration of the drug in the formulation being delivered to the patient. At the same time, the seal must permit smooth operation as the valve stem slides into and out of the metering chamber during actuation of the aerosol delivery device.
One problem observed in MDIs is that sharp edges of the side hole can damage the diaphragm upon repeated actuation of the MDI. Damage to the diaphragm is observed regardless of whether the valve stem is made of metal or plastic. Such damage to the diaphragm can degrade the seal between the diaphragm and the valve stem, thereby corrupting dose metering and contaminating the aerosol with particles of diaphragm material. Damage to the diaphragm may also block or partially block delivery of the aerosol. This may occur directly, such as by accumulation of diaphragm fragments. Alternatively, the effect may be indirect; the abraded particles may act as xe2x80x9cseedingxe2x80x9d for crystallization of the aerosol. Delivery of the aerosol may be completely or partially blocked by accumulated diaphragm particles, crystallized aerosol, or both.
One approach to solve the problem of damage to the diaphragm by the edges of the side hole is to provide a side hole with rounded or beveled edges. This is done deliberately during the manufacture of metal valve stems. When the side hole is punched into the valve stem, the surrounding metal is bent inward, resulting in rounded edges. International Publication No. WO 99/55600 describes side hole edges that are drilled, then countersunk in order to obtain rounded edges. No equivalent shaping of the side hole edges has been applied to plastic valve stems.
Damage to the diaphragm still has been observed in aerosol delivery devices, even those having a side hole with rounded or beveled edges. Therefore, a continuing need exists for an aerosol valve stem that reduces damage to the diaphragm upon repeated actuation.
It has now been found that the geometry of a round hole on a cylindrical surface is an important contributor to the damage done to the diaphragm upon actuation of a metered dose aerosol delivery device, even when the side hole has rounded or beveled edges. The aerosol valve stem configuration of the present invention significantly reduces diaphragm seal abrasion.
The valve stem of a metered dose aerosol delivery device is generally cylindrical and the side hole is positioned perpendicular the valve stem axis. Because the side hole is located on a cylindrical surface, the edges of the side hole define a shape similar to that of a saddle, presenting sharp edges at the top and the bottom of the side hole. These sharp edges have a tendency to damage the surface of the diaphragm each time the side hole passes through the diaphragm aperture. After repeated actuation of the device, the damage can be sufficient to cause particles to be abraded from the diaphragm, thereby reducing sealing performance. Such damage to the diaphragm also results in particles contaminating the aerosolized medicine being delivered to the patient.
Rounded or beveled edges of the side hole do not eliminate degradation of the diaphragm by the edges of the side hole; the side hole edges still possess the raised profile of the saddle shape inherent in a round hole on a cylindrical surface.
The present invention provides an aerosol valve stem in which the area around the side hole is flattened. The invention is particularly well suited for use in a metered dose aerosol delivery device such as an MDI, because the edges of the side hole define a planar circle or, at least, a very shallow saddle. The geometry of the side hole minimizes abrasion of the diaphragm as the side hole passes through the diaphragm aperture.
One embodiment of the invention provides a generally cylindrical aerosol valve stem having a tip at one end and a body wall defining a hollow core extending axially from the tip into the body. A side hole pierces the body wall of the valve stem and is in communication with the hollow core. Finally, there is a flattened area around the side hole so that abrasion of the diaphragm gasket by the edges of the side hole is reduced.
The edges of the side hole may be rounded or beveled in order to further decrease the abrasive effects of the side hole passing through the diaphragm aperture. The flattened area may be so flattened so as to provide a planar surface surrounding the side hole. In one configuration, the flattened area may be limited to the area adjacent to the side hole. Alternatively, the flattened area may extend to the tip of the valve stem, into the sealing area of the valve stem, or both. In each configuration, the aerosol valve stem of the invention significantly reduces diaphragm seal abrasion.
Another embodiment of the invention provides a metered dose valve including an aerosol valve stem as described above.
Another embodiment of the invention provides for a metered dose inhaler including an aerosol valve stem as described above.
Accordingly, the present invention provides an aerosol valve stem including: a generally cylindrical body having a tip at one end and a body wall defining a hollow core extending axially from the tip into the body, a side hole through the body wall in fluid communication with the hollow core, and a flattened area around the hole.
In another aspect the invention provides a device for delivering an aerosol including: a generally cylindrical body having a tip at one end and a body wall defining a hollow core extending axially from the tip into the body, a side hole through the body wall in fluid communication with the hollow core, and a flattened area around the hole; a diaphragm having walls defining a diaphragm aperture; a casing member having walls defining a formulation chamber and a casing aperture; wherein the valve stem passes through the diaphragm aperture and the casing aperture and is in slidable sealing engagement with the diaphragm aperture, and wherein the diaphragm is in sealing engagement with the casing member; and a metering chamber of a predetermined volume and having an inlet end, an inlet aperture and an outlet end, wherein the outlet end is in sealing engagement with the diaphragm, and wherein the valve stem passes through the inlet aperture and is in slidable engagement with the inlet end of the metering chamber, and wherein the valve stem is movable between an extended, closed position, in which the inlet end of the metering chamber is open and the outlet end is closed, and a compressed, actuated position in which the inlet end of the metering chamber is closed and the outlet end is open.
In yet another aspect, the invention provides a method of delivering an aerosolized dose of medicine including the steps of: providing an inhaler including an aerosol valve stem including a generally cylindrical body having a tip at one end and a body wall defining a hollow core extending axially from the tip into the body, a side hole through the body wall in fluid communication with the hollow core, and a flattened area around the hole; providing a formulation of aerosolized medicine contained within the inhaler; and actuating the inhaler.